Lenovo G550 Vista laptop audio problem

Hello,
Sent my laptop to computer firm with suspected virus. returned with the comment that there was no virus, but they had cleaned out any junk files. Subsequently found that there was no audio although the audio cards are there. Back to the comp firm who now want to completely clean and re-install everything, as they can't fix the audio, at an additional charge.
The audio shows a red cross next to it. Help please.